The present disclosure relates to processes for preparing polyestercarbonate (PEC) compositions. In this regard, the disclosure relates to the interfacial synthesis of polyestercarbonates and to compositions produced by such processes.
Polycarbonates (PC) are synthetic thermoplastic resins derived from bisphenols and phosgene, or their derivatives. They are linear polyesters of carbonic acid and can be formed interfacially from reaction of dihydroxy compounds with phosgene or via ester interchange by reaction of dihydroxy compounds with a carbonate diester.
The desired properties of polycarbonates include clarity or transparency (i.e. 90% light transmission or more), high impact strength and toughness, heat resistance, weather and ozone resistance, good ductility, being combustible but self-extinguishing, good electrical resistance, noncorrosive, nontoxic, etc. They are useful for forming a wide array of products, such as by molding, extrusion, and thermoforming processes.
In producing a polycarbonate, a homopolycarbonate is generally formed from the polymerization of a dihydroxy compound such as bisphenol-A. However, when a dicarboxylic acid is copolymerized with bisphenol-A, a polyestercarbonate results. A variety of dicarboxylic acids have been copolymerized with bisphenol-A to form various polyestercarbonates. Such polyestercarbonates generally have lower glass transition temperatures, better melt flow rates, and better ductility relative to a bisphenol-A homopolymer.
Adipic acid (also known as hexanedioic acid; 1,4-butanedicarboxylic acid; HOOC—(CH2)4—COOH) is perhaps one of the most desirable dicarboxylic acids to copolymerize with bisphenol-A. This is due, in part, to its low cost. However, short chain dicarboxylic acids like adipic acid are difficult to incorporate into polyestercarbonates. Poor incorporation of adipic acid can create undesirable quality issues, while incomplete incorporation leaves residual adipic acid in process streams that can adversely affect downstream operations.
Short chain dicarboxylic acids have been successfully incorporated via interfacial polymerization when used in an activated form, such as the acid chloride or anhydride form. See, for example, U.S. Pat. No. 5,015,720. However, these activated forms are more expensive than the simple dicarboxylic acid. In addition, they may contain color contaminants that cause the final polymer to be highly colored. This is undesirable for applications in which a transparent or low color polymer composition is sought.
U.S. Pat. No. 5,274,068 describes methods for producing polyestercarbonates via interfacial polymerization using simple dicarboxylic acids like adipic acid. The examples achieve a range of 17% to 99% incorporation of adipic acid. This large variation suggests that some critical process variables have not been identified. Such variation is also usually unacceptable for commercial manufacturing processes. In particular, the wide range of incorporation occurs with only small changes in the amount of time for which reactions were allowed to occur.
Accordingly, it is desirable to generate new processes that allow for consistent incorporation of high levels of adipic acid into a polyestercarbonate.